I didn't actually read this anywhere, so i might be wrong, but it would make more sense for it to be constriction. Sympathetic innervation is more for special situations, when you have bigger things to worry about than filtering blood.

"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

We have different kinds of receptors in our vessel cells. Some might constrict like digestive and some might dilate like muscle vessels. But the work of kidney is not only filtering blood. It's other function is to regulate blood pressure. So I think it would dilate because of high blood pressure